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Abstract
Photographic and mobile-radar documentation of the dissipation of a supercell and a severe convective storm that had not yet developed into a mature supercell are discussed. It is hypothesized, based on these cases and on others, that when a low-precipitation or classic supercell and/or a developing supercell moves into an environment of cooler surface temperatures and a strong capping inversion, it eventually dissipates through a process of “downscale transition,” in which vertical shear tilts the updraft more in the downshear direction as the CAPE decreases, and the updraft becomes narrower as the storm dissipates. During the downscale transition, it is possible that a cold pool or lack thereof may play a role, but the documentation in the cases detailed herein is not adequate to address this issue.
Abstract
Photographic and mobile-radar documentation of the dissipation of a supercell and a severe convective storm that had not yet developed into a mature supercell are discussed. It is hypothesized, based on these cases and on others, that when a low-precipitation or classic supercell and/or a developing supercell moves into an environment of cooler surface temperatures and a strong capping inversion, it eventually dissipates through a process of “downscale transition,” in which vertical shear tilts the updraft more in the downshear direction as the CAPE decreases, and the updraft becomes narrower as the storm dissipates. During the downscale transition, it is possible that a cold pool or lack thereof may play a role, but the documentation in the cases detailed herein is not adequate to address this issue.
Abstract
Premodification of the atmosphere by upwind lakes is known to influence lake-effect snowstorm intensity and locations over downwind lakes. This study highlights perhaps the most visible manifestation of the link between convection over two or more of the Great Lakes lake-to-lake (L2L) cloud bands. Emphasis is placed on L2L cloud bands observed in high-resolution satellite imagery on 2 December 2003. These L2L cloud bands developed over Lake Superior and were modified as they passed over Lakes Michigan and Erie and intervening land areas. This event is put into a longer-term context through documentation of the frequency with which lake-effect and, particularly, L2L cloud bands occurred over a 5-yr time period over different areas of the Great Lakes region.
Abstract
Premodification of the atmosphere by upwind lakes is known to influence lake-effect snowstorm intensity and locations over downwind lakes. This study highlights perhaps the most visible manifestation of the link between convection over two or more of the Great Lakes lake-to-lake (L2L) cloud bands. Emphasis is placed on L2L cloud bands observed in high-resolution satellite imagery on 2 December 2003. These L2L cloud bands developed over Lake Superior and were modified as they passed over Lakes Michigan and Erie and intervening land areas. This event is put into a longer-term context through documentation of the frequency with which lake-effect and, particularly, L2L cloud bands occurred over a 5-yr time period over different areas of the Great Lakes region.
Abstract
Anticyclonic left-moving supercells are observed each year in the United States, emanating both discretely and from storm splitting processes. Such thunderstorms often produce severe hail and wind gusts and, on rare occasion, tornadoes. The body of documentary literature on this subset of supercells is relatively scant compared with right-moving storms, and this is especially true regarding visual characteristics and conceptual models. Here a characteristic example of the anticyclonic supercell is presented using an intense and well-defined specimen that passed over Aroya, Colorado, on 15 June 2002. Photographic and radar documentation is provided in original and mirrored forms, for aid in conceptualizing the left-moving supercell and associated structures and processes. A summary overview is presented of the environment, development, evolution, and effects of this remotely located but noteworthy event.
Abstract
Anticyclonic left-moving supercells are observed each year in the United States, emanating both discretely and from storm splitting processes. Such thunderstorms often produce severe hail and wind gusts and, on rare occasion, tornadoes. The body of documentary literature on this subset of supercells is relatively scant compared with right-moving storms, and this is especially true regarding visual characteristics and conceptual models. Here a characteristic example of the anticyclonic supercell is presented using an intense and well-defined specimen that passed over Aroya, Colorado, on 15 June 2002. Photographic and radar documentation is provided in original and mirrored forms, for aid in conceptualizing the left-moving supercell and associated structures and processes. A summary overview is presented of the environment, development, evolution, and effects of this remotely located but noteworthy event.
Abstract
A photograph of vertically aligned Kelvin–Helmholtz billows in the eastern eyewall of Hurricane Erin on 10 September 2001 is presented. The vertical shear instability in the horizontal winds necessary to produce the billows is confirmed with a high-altitude dropwindsonde observation. This shear instability is not known to be common in tropical cyclone eyewalls and is likely only in cases with a very large eyewall tilt. However, research and reconnaissance aircraft pilots need to be aware of the possibility of their existence, along with other types of hazardous conditions, in such rare circumstances.
Abstract
A photograph of vertically aligned Kelvin–Helmholtz billows in the eastern eyewall of Hurricane Erin on 10 September 2001 is presented. The vertical shear instability in the horizontal winds necessary to produce the billows is confirmed with a high-altitude dropwindsonde observation. This shear instability is not known to be common in tropical cyclone eyewalls and is likely only in cases with a very large eyewall tilt. However, research and reconnaissance aircraft pilots need to be aware of the possibility of their existence, along with other types of hazardous conditions, in such rare circumstances.
Abstract
In this brief contribution, photographic documentation is provided of a variety of small, tubular-shaped clouds and of a small funnel cloud pendant from a convective cloud that appears to have been modified by flow over high-altitude mountains in northeast Colorado. These funnel clouds are contrasted with others that have been documented, including those pendant from high-based cumulus clouds in the plains of the United States. It is suggested that the mountain funnel cloud is unique in that flow over high terrain is probably responsible for its existence; other types of small funnel clouds are seen both over elevated, mountainous terrain and over flat terrain at lower elevations.
Abstract
In this brief contribution, photographic documentation is provided of a variety of small, tubular-shaped clouds and of a small funnel cloud pendant from a convective cloud that appears to have been modified by flow over high-altitude mountains in northeast Colorado. These funnel clouds are contrasted with others that have been documented, including those pendant from high-based cumulus clouds in the plains of the United States. It is suggested that the mountain funnel cloud is unique in that flow over high terrain is probably responsible for its existence; other types of small funnel clouds are seen both over elevated, mountainous terrain and over flat terrain at lower elevations.
Abstract
Several examples of Geostationary Operational Environmental Satellite (GOES) visible satellite images depicting cloud features often associated with the transition to, or intensification of, supercell thunderstorms are presented. The accompanying discussion describes what is known about these features, and what is left to learn. The examples are presented to increase awareness among meteorologists of these potentially significant storm features.
Abstract
Several examples of Geostationary Operational Environmental Satellite (GOES) visible satellite images depicting cloud features often associated with the transition to, or intensification of, supercell thunderstorms are presented. The accompanying discussion describes what is known about these features, and what is left to learn. The examples are presented to increase awareness among meteorologists of these potentially significant storm features.
Abstract
A cold-air outbreak east of the Rocky Mountains on 23 January 2003 produced banded clouds and snow across the central and southeastern United States. The bands occurred through two processes: 1) thermal instability in the planetary boundary layer produced horizontal convective rolls (HCRs) over widespread areas, and 2) lake-effect processes downstream of small lakes (fetch < 100 km) produced localized bands. Characteristics of the observed bands associated with the HCRs, such as horizontal scale, depth of circulation, orientation, duration, and dynamics, are explored through observations, previous literature, and theoretical models. Snow from clouds produced by HCRs over land during the cold season has not been extensively studied previously. In this event, cold-air advection over the warm ground led to an upward sensible heat flux, promoting the occurrence of the HCR circulations. As the surface temperature decreased, the height of the lifting condensation level decreased, eventually forming cloud bands within the ascending portion of the HCR circulations. Ice crystals are inferred to have fallen from a large-scale precipitation system aloft into the cloud bands in the planetary boundary layer, which was within the favored temperature regime for dendritic growth of ice crystals. The ice crystals grew and reached the surface as light snow. This seeder–feeder process suggests one way to anticipate development of such snowbands in the future, as demonstrated by other similar events on other days in Oklahoma and Illinois. As the cloud bands were advected equatorward, they ingested drier air and dissipated. Among the several lake-effect bands observed on 23 January 2003, one notable band occurred downwind of Lake Kentucky. Midlake convergence of the land breeze may have initially produced a narrow cloud band that broadened as the land breeze ended. That the snowbands due to the HCRs and lake effect were both associated with heat and/or moisture fluxes from the earth's surface highlights the potential importance of ground- and water-surface temperature measurements for accurate numerical weather prediction.
Abstract
A cold-air outbreak east of the Rocky Mountains on 23 January 2003 produced banded clouds and snow across the central and southeastern United States. The bands occurred through two processes: 1) thermal instability in the planetary boundary layer produced horizontal convective rolls (HCRs) over widespread areas, and 2) lake-effect processes downstream of small lakes (fetch < 100 km) produced localized bands. Characteristics of the observed bands associated with the HCRs, such as horizontal scale, depth of circulation, orientation, duration, and dynamics, are explored through observations, previous literature, and theoretical models. Snow from clouds produced by HCRs over land during the cold season has not been extensively studied previously. In this event, cold-air advection over the warm ground led to an upward sensible heat flux, promoting the occurrence of the HCR circulations. As the surface temperature decreased, the height of the lifting condensation level decreased, eventually forming cloud bands within the ascending portion of the HCR circulations. Ice crystals are inferred to have fallen from a large-scale precipitation system aloft into the cloud bands in the planetary boundary layer, which was within the favored temperature regime for dendritic growth of ice crystals. The ice crystals grew and reached the surface as light snow. This seeder–feeder process suggests one way to anticipate development of such snowbands in the future, as demonstrated by other similar events on other days in Oklahoma and Illinois. As the cloud bands were advected equatorward, they ingested drier air and dissipated. Among the several lake-effect bands observed on 23 January 2003, one notable band occurred downwind of Lake Kentucky. Midlake convergence of the land breeze may have initially produced a narrow cloud band that broadened as the land breeze ended. That the snowbands due to the HCRs and lake effect were both associated with heat and/or moisture fluxes from the earth's surface highlights the potential importance of ground- and water-surface temperature measurements for accurate numerical weather prediction.
